Bindi Irwin Celebrates Brother Robert's Birthday With Heartfelt Throwback Photo

Bindi Irwin, Robert Irwin

Bindi Irwin celebrated her not-so-little brother Robert's birthday with the sweetest message.

Robert turned 20 on Dec. 1 and to honor his special day, his big sister Bindi shared a montage of throwback photos from over the years, including one from when the two were kids. Alongside the adorable pictures, Bindi penned a loving message in the caption and set Friday's post to the tune "Call Your Sister" by Taylor Edwards.

In the first snap, 10-year-old Bindi towered over her younger brother, who was only 5, as the two children posed for the camera. Before moving on to the next image, an overlay of text popped up on the screen, which read: "Fast forward 15 years."

The second slide featured a more recent photo of the two, showing just how much they have grown up as Robert is now a full head over his sister–a comment Bindi must always hear as she joked about it in the caption.

"Now I’m standing on my tiptoes to take a photo with you," she quipped. "Happy birthday to the best. 20 years, and a lifetime of adventures ahead of you - remember, you can always call your sister. Love you @robertirwinphotography."

Robert later replied in the comments, returning the admiration to his sister. "Aw this is the BEST ????," he wrote. "Love you Bindi!!! Bring on the next 20 ??."

Fans were just as ecstatic over the post, sharing their love for the nature-loving brother-sister duo in the replies.

"This is the best Bindi! ????," cheered Robert's girlfriend, Rorie Buckey.

"You two are fab. Your dad would be so bloody proud," another top-liked comment read. "Happy birthday. ??????."

"You two are an amazing pair of siblings," someone else added. "Happy birthday Robert! ?? ??."

Next: Bindi Irwin Shares Touching Throwback to Honor Late Father Steve